Naval Surface Warfare Center

About: Naval Surface Warfare Center is a facility organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Radar & Sonar. The organization has 2855 authors who have published 3697 publications receiving 83518 citations. The organization is also known as: NSWC.

Magnetomechanical damping in giant magnetostriction alloys

Abstract: Magnetomechanical damping in the giant magnetostriction material Terfenol-D has been investigated by quasi-static stress-strain measurements and modeled theoretically. The damping capacity is a strong function of applied stress amplitude, increasing to a maximum at some finite stress and then decreasing slowly at still larger applied stresses. Maximum damping capacities greater than 1.0 were observed for the lowest magnetic bias fields and prestresses at applied stress amplitudes of 4 MPa. Both the qualitative behavior of the damping and its magnitude are successfully described by a model of abrupt magnetization jumps within individual domains driven by the applied stress.

Start up performance of load-commutated inverter fed synchronous machine drives

Abstract: Load-commutated inverter (LCI) synchronous machine drives are common in the high power range. However, the starting performance of these systems is a concern since load-commutation cannot occur at arbitrarily low speeds. This paper compares three different starting strategies including one apparently neglected method-normal load commutation. In particular, it is shown that, depending on system parameters, it may be possible to start the system with no special provision for start up. A method to determine whether a given system can be started using load commutation is presented. >

Contact angle anomalies indicate that surface-active eluates from silicone coatings inhibit the adhesive mechanisms of fouling organisms.

Abstract: Silicone coatings with critical surface tensions (CST) between 20 and 30 mN m-1 more easily release diverse types of biofouling than do materials of higher and lower CST. Oils added to these coatings selectively further diminish the attachment strengths of different marine fouling organisms, without significantly modifying the initial CST. In a search for the mechanisms of this improved biofouling resistance, the interfacial instabilities of four silicone coatings were characterised by comprehensive contact angle analyses, using up to 12 different diagnostic fluids selected to mimic the side chain chemistries of the common amino acids of bioadhesive proteins. The surfaces of painted steel test panels were characterised both before and after exposure to freshwater, brackish water, and seawater over periods ranging from 9 months to nearly 4 years. Contact angle measurements demonstrated significant surface activity of the oil-amended coatings both before and after long-term underwater exposure. The surface activity of the control (coating without oil) increased as a result of underwater exposure, consistent with mild surface chain scission and hydrolysis imparting a self-surfactancy to the coating and providing a weak boundary layer promoting continuing easy release of attaching foulants. Coatings with additives that most effectively reduced biofouling showed both initial and persistent contact angle anomalies for the test liquid, thiodiglycol, suggesting lower-shear biofouling release mechanisms based upon diminished bioadhesive crosslinking by interfering with hydrogen- and sulfhydryl bonds. Swelling of the silicone elastomeric coatings by hydrocarbon fluids was observed for all four coatings, before and after immersion.